1. Field of the Invention
The present invention relates to a diamond-metal junction product in which a diamond semiconductor and a metal are integrated through an ohmic junction.
2. Description of the Related Art
In general, diamond has a large band gap of about 5.5 eV and a large carrier mobility (1800 cm.sup.2 /V.multidot.S for electrons and 1600 cm.sup.2 /V.multidot.S for holes), as well as a large thermal conductivity of about 20 W/cm.multidot.k. In addition, diamond exhibits a very high level of hardness and, hence, superior wear resistance. Thus, diamond possesses various advantageous properties which can never be offered by other materials.
In recent years, remarkable progress has been achieved in the technique for synthesizing diamond from gaseous phases, and it is now possible to form a diamond film by chemical vapor deposition (CVD).
Studies also have been made to develop a technique for producing semiconductors by doping diamond crystals with impurities. Shiomi et al. reported that a field effect transistor can be produced by forming, on an artificial diamond substrate, a diamond film containing boron as an impurity by a vapor synthesis technique and then forming Schottky junction metal and ohmic junction metal.
Hitherto, however, it has been difficult to form metal electrodes on diamond crystal by diamond-metal junction with a high degree of reproducibility of the characteristics of the product. Namely, characteristics of a diamond-metal junction material largely vary according to factors such as the conditions for forming the diamond, the conditions of processing after formation of the diamond and the methods of forming the electrodes.
For instance, whether the type of junction formed is an ohmic junction or a Schottky junction depends on whether a methane-hydrogen type gas or a carbon monoxide-hydrogen type gas is used as the material gas in forming the diamond. It is also known that a metal junction which has exhibited an ohmic nature is changed into a metal junction exhibiting a Schottky nature when diamond crystal is scrubbed with a chromic acid mixed solution. Characteristics also vary largely depending on whether the metal electrode is formed to make a point conduct or evaporation-deposited on the diamond layer.
Thus, it has been difficult to obtain a product having metal electrodes by a diamond-metal junction with a high degree of reproducibility.